The effects of partial defoliation on the gas exchange characteristics of the remaining leaves were studied in cloned Betula pendula L. saplings grown in pots on two different soil types: prefertilized peat and unfertilized sand (Experiment 1). The responses of undamaged leaves to different damage modes of leaf laminae were also studied using saplings grown on prefertilized peat only (Experiment 2). In Experiment 1, removal of the upper leaves, which represented about half the total leaf area, approximately doubled the mean net photosynthetic rates of the remaining lower leaves on both soil types and at both measuring dates (12–13 d and 34 d after assigning the treatments). However, when the lower leaves were removed there was a temporary increase in the mean net photosynthetic rates of the remaining expanded upper leaves only in the plants grown on sand. In Experiment 2, the removal of laminae caused a similar increase in the light-saturated net photosynthetic rates of the remaining leaves, irrespective of whether the laminae were removed totally immediately or gradually in three stages. The magnitude of the photosynthetic response was determined by the amount of leaf tissue removed and was independent of the way in which it was removed. We conclude that the increase in the photosynthetic rates of the remaining leaves after partial defoliation may be attributed to the alleviated competitive status among the leaves rather than to the decreased source/sink ratio within a plant.